From what I have seen of him as an on-air expert for MSNBC, he would be a great choice. I remember early in the drive to Baghdad, he and Brian Williams were on a Chinook that was forced down in a sand storm. An Infantry platoon happened to be in the area and provided security for the craft and personnel for about 24 hours. He related the story of how the Platoon Leader reacted when he found out Downing was a retired O-10. Pretty funny.
He is very capable and seems to have this rare capacity for focusing on his mission and getting it done with causing political uproar.
Homeland Security needs a security expert in charge.